Shinobu fujiwara
ceramic dielectrics



Oct. 31', 1967 sHlNoBu FUJIWARA 3,350,212

CERAMIC DIELECTRICS Filed' May 12, 1964 2 Sheets-Sheet 1 mig] i M/M Mugs,

OC- 31 1957 sHiNoB'U FUJIWARA 3,350,212

v CERAMIC DIELECTRICS Filed May 12, 1964 /t/y- 5- 4 smo;

2 Sheets-Sheet 2 540i-m02 @0 60 4o 20 1205 A INVENTOR.

BY aff-MVM VZ United sat-@S Patent o ABSTRACT OF THE DISCLOSURE The present invention provides ceramic dielectric materials having high dielectric constants, low dielectric losses and small temperature coeicients of dielectric constants. The materials consist essentially vof a sintered mixture comprising SrTiO3 in an amount of from 40 to `75% by weight, Bi2O32TiO2 in an amount of from 10 to 50% by weight and LaZOa in an amount of from 5 to 20% by weight. In one aspect of the invention, the SrTiO3 employed is prepared by admixing SrTiO3 with about 0.3% of manganese sulfate as a mineralizer and pre-sintering the mixture at a temperature of about 1300 C. The ceramic dielectric materials are useful in manufacturing of small sized capacitors.

The present invention relates to improvements in certain of the properties of ceramic dielectrics.

The object of the present invention is to provide ceramic dielectrics which show high dielectric constants, low dielectric losses and small temperature coe'icients of dielectric constants, and these dielectric materials have advantages for making small sized capacitors which are stable to temperature changes and have small values of tan andvery low strain inductances.

As well known, ceramic' dielectrics which comprise mainly barium titanate (BaTiO3) are most widely used where highly dielectric materials are required. But a dielectric material of this kind shows a very steep curve against dielectric constant as a function of temperature, at its Curie point which lies around 120 C. Therefore, it cannot be used for the kind of purposes that require a fairly constant dielectric constant over a wide temperature region, and this fact extremely limits the practical applications of the said products.

Attempts have been made to remove the sharp change of dielectric constant at the Curie point and to smooth out the temperature characteristics as completely as possible. For example, Curie point can be lowered to room temperature by adding such materials as barium stannate (BaSn03) or barium zirconate (BaZrO3) to barium titanate (BaTiOa), and temperature dependence can be smoothed out to some extent by the addition of such materials as calcium titanate (CaTiO3) or magnesium titanate (MgTiOa). But all these not only fail to attain a satisfactory improvement but also involve the lowering of dielectric constant and Q-value, and because of this fact, the products are not suitable for practical purposes.

According to the present invention, the dieletric materials have improved properties, .e., good temperature characteristics, maintaining high dielectric constants and high Q-values at the same time.

The dielectric materials of the present invention show the desired properties in the following composition:

lCC

The reasons for limiting the composition to said proportions are as follows:

When the proportion of strontium titanate (SrTiO3) exceeds 75% vby Weightthe temperature for sintering requires to be higher than 1400 C. and vitrification be-v comes diflicult, and when it is under 40% by weight, dielectric constant decreases to less than 200 and the products become porous and less dense.

When the mixture of bismuth oxide and titanium oxide (Bi2O3-2TiO2) exceeds 50% by Weight, sintering becomes diilcult with consequent poor vitrication, and Q-Values become low, and when it isunder 10% by weight, the temperature for sintering should be higher than 1380 C. and the vitrication becomes diflcult. When the proportion of La203 exceeds 20% by weight, the vitrication becomes extremely diicult, and when it is under 5%, Q- values become too low.

FIG. 1 in the accompanying drawings show the relation between the dielectric constant and temperature of the highly dielectric materials which have previously been used. Curve A is the dielectric constant-temperature characteristic of a barium titanate (BaTiO3) ceramic showing a very sharp change at the Curie point which lies approximately at C.

Curve B is also the dielectric constant-temperature characteristic of a barium titanate (BaTiO3) ceramic mixed with other material such as barium stannate (BaSnO3) or barium zirconate (BaZrOa), and it is seen that the Curie point is shifted and the dielectric constant change less sharply.

FIG. 2vis the ternary diagram showing the relation between the dielectric constants and the proportions of the three components of the products, strontium `titanate (SrTiOs), mixture of bismuth oxide and titanium oxide (B2( )32TiO2) and lanthanum (III) oxide (La203). Thel i numerical values on the diagram represent the dielectric constants.

FIG. 3 is another ternary diagram showing the relation between the compositions and the temperature coeicients of dielectric constants. The numerical values on the diagram represent the temperature coefficients of dielectric constants.

FIG. 4 is also the ternary diagram which show the relation between the compositions and Q-values, and the numerical values represent the Q-values.

The characteristic values given in FIG. 2, FIG. 3 and FIG. 4 were'measured at 1mc./s.

According to the present invention the products are obtained by the following procedure: A suitable mineralizer such as manganese sulfate (MnSO4) is added to strontium titanate (SrTiO3), and after pre-sintering at about 1300 C., this material is ground into powder and mixed with mixture of bismuth oxide and titanium oxide (Bi2O3-2Ti02) and lanthanum (III) oxide (La203), and nally the desired products are obtained by sintering this mixture. The sintering temperature and hours may be varied, dependent upon the composition.

l Some examples of the present invention are given be- EXAMPLE l Strontium titanate (SrTiO3) is admixed with 0.3% of manganese sulfate (MnSO4), and after pre-sintering at 1320 C., it is ground into powder and mixed with mixture of bismuth oxide and titanium oxide (Bi2O32TiO2) and lafnthanum (III) oxide (La2O3) inthe weight proportion o and the mixture is shaped and then sintered nally at 3 v 1350 C. The ceramic dielectrics thus obtained show the following properties:

Dielectric constant 356 Temperature coefficient of dielectric constant C-- -1775 l06 Q-value 14250 The properties were measured at l mc./s. in all of the examples.

EXAMPLE 2 Strontium titanate (SrTiO3) is pre-sintered at 1320 C. with 0.3% of manganese sulfate (MnSO4), then powdered and mixed with mixture of bismuth oxide and titanium oxide (Bi2O3-2Ti02) and lanthauum (III) oxide (La2O3) in the weight proportion of SrTiOazBiZOS 2TiO2:La2O3=70:25:5 and after being shaped, the mixture is sintered at 1350 C., the resultant products having Vthe following properties:

Dielectric constant 725 Temperature coefficient of dielectric constant C 2370x10-8 Q-value 2800 Dielectric constant 247 Temperature coefficient of dielectric constant C -1505X10-5 Q-value 9000 As shown in the above examples, the dielectric materials in accordance with the present invention have excellent properties in that, while maintaining high diele.-

4 tric constants,` they have small temperature coefficient and high Q-values with their maximum being about 15,000.

I claim: 1. A ceramic dielectric consisting essentially of a sintered mixture of SrTiO3 from 40 to 75% -by weight, Bi2O32TiO2 from 10 to 50% by weight and La2O3 from 5 to 20% by weight.

2. A ceramic dielectricv consisting essentially of a sintered mixture of 56% by Weight of SrTiO3, 35% by weight of Bi2O3-2TiO2 and 9% by weight of La203.

3. A ceramic dielectric consisting essentially of a sintered mixture of 70% by weight of SrTiO3, 25% by Weight of Bi2O3-2Ti02 and 5% by weight of La2O3.

4. A ceramic dielectric consisting essentially of a sintered mixture of by weight of SrTiOs, 40% by weight of Bi2O3-2Ti02 and 10% by weight of La203.

5. A ceramic dielectric material consisting of a sintered mixture of (a) 40 to 75 by weight of SrTiO3 prepared by admixing SrTiO3 with about 0.3% of manganese sulfate as a mineralizer and pre-sintering the mixture at a temperature of about 1320 C.,

(b) 10 to 50% by weight Bi2O3-2TiO2, and

(c) 5 to 20% by weight La203.

References Cited UNITED STATES PATENTS 2,467,169 4/ 1949 Waner 106-39 V3,179,525 5/1965 Welsby et al. 7.--- 106-39 FOREIGN PATENTS 1,178,181 7/1957 France.

OTHER REFERENCES Lapluye et al.-Etfects of Incorporation of Metallic Oxides on Properties of Barium Titanate-Compt. Reno. 250 (2) January 1960, pp. 305-307.

MacChesney et al.-Stabilized Barium Titanate Ceramics for Capacitor Dielectrics-J. Am. Ceramic Soc., vol. 46 1963), pp. 197-202.

HELEN M. MCCAR'IHY, Primary Examiner. 

1. A CERAMIC DIELECTRIC CONSISTING ESSENTIALLY OF A SINTERED MIXTURE OF SRTIO3 FROM 40 TO 75% BY WEIGHT, BI2O3$2TIO2 FROM 10 TO 50% BY WEIGHT AND LA2O3 FROM 5 TO 20% BY WEIGHT. 